Video: Unthinkable scenarios

September 11th seemed a perfect day to fly in the Northeast. Daybreak was crisp and bright. There was unlimited visibility: no ceiling and conditions were just right.

Greg Callahan, Newark air traffic controller: We were very busy, things were moving nicely.

As usual, the skies over America that day were crowded with airplanes. Often 4,000-6,000 are airborne at any given time. For air traffic controllers, keeping them moving safely and on time is an intricately choreographed ballet—each plane moving through the air at different speeds, altitudes, and headings.

Curt Applegate, New York air traffic controller: It is a thing of beauty. It is like clockwork.

Making it all happen is a complex mix of manpower and technology, procedure and judgment. The pressure is constant; the stress, unrelenting.

Despite the computers and training, the backup systems and safety equipment, in the end it is the air traffic controllers who must, at a moment’s notice, make sense of it all. But on this day, nothing would make sense.

Mike Blake, Boston air traffic controller: We’re ingrained to know that you’re gonna be faced with adversity or possibly even death.

Rick Tepper: You always wonder, you know, the law of averages. That sooner or later something’s going to happen. And you just hope that it’s not on your shift.

But for these 20 air traffic controllers, and hundreds of others across the U.S, it did happen on their shift.

Five years ago, the morning of September 11thAir traffic controllers watched in disbelief as four passenger planes were hijacked, back to back, in little more than an hour. They were as stunned as the rest of us—working in uncharted territory, but at the same time, forced to make critical decisions; hundreds of thousand of lives were at risk.

In a special NBC News report they all share their story: what they saw, what they felt as they were witness to the most devastating tragedy in aviation history.

Tom Brokaw, NBC News: How much of that day has lingered with you?

Don Jeffroy: The whole day.

Brokaw: Still think about it?

Jeffroy: Yeah, there’s not a day goes by where you don’t have to think about it.

It all began at Boston’s Logan airport. It’s morning rush hour. Planes are already stacked on the runway, waiting to get final clearance for takeoff.

8:00 am.
American Flight 11, bound for Los Angeles, pushes back from the gate and is cleared for takeoff. The Boeing-767 with 81 passengers, 11 crew and 24 thousand gallons of jet fuel, lifts off, headed west.

As the plane climbs out of Boston Logan, it’s handed off from one air traffic control center to the next. By 8:10 a.m., American Flight 11 is in the hands of Boston’s regional “en route” center which is located 50 miles outside the city.

More than 75 controllers are on duty at the time. Among them, Tom Roberts, Lino Martins, Don Jefroy, John Hartling, Pete Zalewski, and Mike Blake.

Within minutes, the 767 is climbing through 20,000 feet, and onto Pete Zalewski’s radar.

8:14 am.: 14 minutes since take-off
American 11 is headed up to its cruising altitude of 35,000 feet, but not before Zalewski radios the pilot a routine order to turn, to keep enough space between American 11 and another plane.

Zalewski: I turn him to 20 degrees right, he took the turn. I then told American 11, “Climb and maintain flight level three-five-zero, 35,000 feet.” There was no response.

Zalewski: At that point, I was just thinking that it was, you know, maybe the pilots weren’t paying attention, or there’s something wrong with the frequency.

Zalewski followed procedures, continuing to try to raise American 11 on the frequency.

Zalewski: And at first, it was pretty much, you know, American 11, you know, “Are you paying attention? Are you listening?” And there was still no response. I used the emergency frequency to try and get a hold of him through that. There was no response.

By now Zalewski is running a mental checklist, trying to account for the loss of communication — a technical problem or maybe a mistake on the pilot’s part?

Zalewski: I went back the previous sector to see if the pilot had accidentally flipped the switch back over on the radio. At that point there was still nothing. We weren’t hearing from him.

American 11 was “NORDO”—“no radio contact.” Zalewski stepped up his efforts.

Zalewski: I would go on to call that aircraft 12 times.

And as it went on, I begin to get more concerned.

Brokaw: You’re watching American 11 at that point as well, Lino?

Lino Martins: Yes. He was in my air space at that time.

Colleague Lino Martins, working nearby, is now also tracking the American Airlines plane.

Lino Martins: I saw him start the right turns, figuring Pete was gonna climb him and that’s when Pete called. And said, “No, he’s staying at two-nine-zero, ‘cause he didn’t respond, he’s NORDO.”

Zalewski: I said, “We’re not talking to him. And he was last assigned at 29, but he may have heard the 35. I’m not sure what he might do here, so just watch him.”

But the second controller did have incoming flights directly in the path of American 11.

Martins: I had to plan ahead on this new heading he was on. He was opposite direction with my Boston arrivals. And I had to get them underneath him.

But then, 8:20 a.m., American 11 abruptly changes course, turning to the northwest.

Zalewski: I then saw the transponder shut off.

Martins: And I’m thinking, “Well, maybe there’s really something wrong. First there’s no radio, now we lost this transponder.”

Every commercial airplane is equipped with a transponder that transmits a constant signal. The signal gives controllers on the ground a steady flow of information—displayed on radar screens in a “datablock” such as this one. Think of it as the airplane’s vital signs containing the carrier, flight number, speed and altitude. If the transponder’s not working, the plane is simply blip on radar. Controllers can see only the location, and the speed of the plane.

Zalewski: And so, I very quietly turned to the supervisor and I said, “Would you please come over here?” I said, “I think something is seriously wrong with this plane.”

Brokaw: Did you suspect hijacking at that point?

Zalewski: Absolutely not. No way.

American 11 has been NORDO for six minutes, and now other controllers are becoming concerned. Tom Roberts tries yet another method to contact the plane.

Tom Roberts: I happened to be working on another American flight on my frequency. One of our procedures or protocols is to go aircraft to aircraft on a company frequency, to see if the pilots from one flight could talk to the pilots of another flight.

But that too, fails. There is still no reply — the silence increasingly ominous as the jet, now drastically off course, flying in a northwesterly direction, toward Albany, New York. Controllers are scrambling to keep create a safe zone around the runaway plane, moving every other flight in the area out of the way, from the ground, all the way up to 35,000 feet.

Roberts: We had pretty much moved all the airplanes from Albany to New York to Syracuse, New York out of the way because that’s the track he was going on.

Martins: And I didn’t know if he was gonna turn back on course...

Roberts: And we had no altitude information. So, it’s not just clearing the altitudes of conflicting traffic...

Martins: It was that whole altitude stratum from the ground, up to 35,000.

8:24 am.: Ten minutes since losing contact.
Controllers see the plane make another unauthorized turn, this time to the left, going south.

Zalewski: And that’s when I heard the first transmission from the aircraft. And I wasn’t quite sure what it was. Because it was just a foreign voice. It was something very different. To me, it sounded almost Middle Eastern.

And I asked, “American 11, is that you? American 11, are you trying to call me?” And then came the next transmission. And in that transmission, I immediately knew something was very wrong. And I knew it was a hijack.

Brokaw: And what did you hear?

Zalewski: I remember the part of them saying they were going back to the airport. And by that, I deduced that they were going to go back to Boston. That’s what I was thinking. And I didn’t believe it was one of the American pilots on board. I immediately stood up and yelled at the supervisor, “John, get over here immediately right now.” And I can just remember everybody in that building, and they were all just looking at me, like, “What is wrong with you?”

Zalewski cannot make out exactly what the hijackers are saying, but the tone of their voices alone, chills him.

Zalewski: I felt from those voices the terror. For some reason, I knew something seemed worse than just a normal hijack. It just seemed very different to me.

Zalewski immediately asks for an assistant, to help listen to the transmissions coming from the plane and puts the frequency on a speaker so others can hear. And, he notifies the supervisor there is a hijacking—the first one on a U.S. carrier in more than a decade.

8:30 am. As Boston Center supervisors notify the FAA and other air traffic centers about the hijacking of American Flight 11, the plane makes another dramatic turn—south towards New York City. Pete Zalewski anxiously listens on the frequency, thinking the hijackers might try to make contact.

Pete Zalewski: Then comes a third transmission from the aircraft. And that one was pretty horrifying.

Zalewski, concerned he might be missing vital information, asks the supervisor to have someone pull the transmission tapes that are automatically recorded, right away.

Zalewski: And thankfully, they did pull the tapes. And a part that I didn’t hear which was, “We have more planes,” or something to that effect. And that really was a key statement.

Don Jeffroy: I’ve heard a number of different tapes in the past of aircraft crashes—and this was in my mind the worst. I’d never heard something like that.

Tom Brokaw, NBC News: Was it just cold blooded?

Jeffroy: It made you actually step up and think: What did he mean, what’s going on? What's next?

The voice they’re most likely hearing is that of Mohammed Atta, who would later come to be known as the mastermind of the terrorist attacks. Controllers believe the hijackers mean to speak to the passengers, mistakenly, keying the mike to air traffic control, and Pete Zalewski instead.

By now American 11 had crossed into airspace John Hartling controls.

John Hartling: And Tom came over and told me that "this aircraft, we believe, is hijacked."

Brokaw: What’d you think when he said the word “hijack?”

Hartling: I didn’t believe him. Because I didn’t think that that stuff would happen anymore, especially in this country.

The plane is now speeding south at almost 600 miles an hour, far faster than the 450 miles an hour it should have been flying. With no transponder information, controllers were now asking the assistance of another plane heading to the west coast that morning. It is United Flight 175.

Hartling: I said, “I’d like you to look at your 12 or one o’clock. Tell me if you see an American 767.” And he said, “Yeah, he’s about 28, 29,000.”

The United flight that Hartling is speaking to had also taken off from Boston’s Logan airport, only 14 minutes after American 11. In fact, it is also a Boeing-767, fully fueled, bound for Los Angeles. It is carrying 58 passengers and 6 crew. Hartling has no way of knowing that five terrorists are also on board this plane, only moments away from making their move.

Hartling: I said, “Well, turn 30 degrees to the right. I wanna make sure I keep you away from this guy,” because I had no idea where he was going.

Brokaw: So you’re still in touch with the pilots in that cockpit.

Hartling: Yeah.

Now that the second United plane is safely back on course, or so he thought, John Hartling hands it off to the next link in the air traffic chain — the New York area en route center.

Brokaw: And you’re keeping your eye on American 11? Now he’s going at a very high rate of speed?

Hartling: No, his speed started to drop drastically.

Brokaw: And what did that say to you?

Hartling: That he wasprobably descending.

Descending rapidly, headed in the direction of New York.

At the New York en route center in Islip, Long Island, Dave Bottiglia, Curt Applegate, and Mark Dipalmo are working a routine shift, no idea what is about to come their way.

By now, American 11 is crossing out of Boston’s airspace, and is bearing down on Bottiglia’s territory in New York. Within seconds the plane—or “target” as controllers call it— appears on his screen.

Bottiglia: The controller right next to me gets up and walks over to me and he says, “You see this target here? He says, “This is American 11. Boston Center thinks it’s a hijack.”

Brokaw: So what’d you think at that point? What was going through your mind?

Bottiglia: I really thought they were probably going to Cuba.

Brokaw: So you kept track of the target?

Bottiglia: Kept track of the target. And now we of course we know he was descending at a rapid pace, but we had no altitude or anything on him.

Within minutes, American 11 simply disappears from radar.

8:46 a.m.

Bottiglia: The only thing I can remember is when the American target disappeared all I said was “Well, we know he’s not high altitude anymore.”

But within seconds, Bottiglia has another unexpected problem. As he and other controllers search the radar, looking for American 11, he suddenly notices that United Flight 175, which moments ago helped him locate the hijacked plane, also has disappeared. Instinctively, Bottiglia knows the two are somehow related. He asks another controller to take over all of his other planes.

Bottiglia: I think my voice was shaking, “Please just take everything and don’t ask any questions.”

He calls the United plane several times unsuccessfully, sharing the same anxiety his colleagues in Boston had felt only moments earlier.

Curt Applegate is working at the next radar bank in the New York center.

Applegate: I could hear them talking behind me and and I realized he had two lost airplanes. That made me very nervous.

Bottiglia: I know something bad’s happening. I really don’t know what. We had no transmissions from United.

Applegate: When I turned back to look at the radar, there was a target right over Allentown. So I turned and yelled at Dave. I thought that was his American that he was looking for.

Brokaw: But you, in fact are looking at the United flight?

Applegate: But I was in fact looking at United, that’s correct.

A transponder signal quickly reappears on radar, somewhere near the New Jersey Pennsylvania border. A mistake , perhaps, on the part of the hijackers— the signal continues to transmit information to controllers. There no longer is any question in Bottiglia’s mind that he’s looking at a second hijacked airliner.

Applegate: When I saw it, it was at 33,000. And as soon as I said that he started to turn to the left. And descending.

United 175 is no longer heading west as it should be. Instead, it has now also turned ominously toward the east, and New York City.

There are now two hijacked airliners in the skies over the East coast—the first, American 11, has already disappeared from radar. Controllers don’t know where it is. The second is United 175, now over northern New Jersey suburbs.

And in Newark, New Jersey, a third plane, and group of controllers will be pulled into the unfolding drama. Dan D’Agastino is a controller at the Newark tower.

The morning shift is running smoothly, other than the usual ground delays at Newark.

Greg Callahan: We had about 25 to 30 planes at the runway at any given moment...

Greg Callahan is clearing planes to take off and land. Only five minutes earlier, at 8:41 a.m., he had cleared a United plane to take off for San Francisco. It had been waiting on the runway, and by the time it took off, it was almost 40 minutes late.

At the time, Callahan had no reason to give it a second thought, but the story of what would happen on that airliner, the bravery and heroism of 33 passengers and 7 crew, would become legend. It was United Flight 93.

But minutes after Flight 93 takes off, uneventfully, something does grab the attention of Newark controllers, whose view from the top of the tower is a panorama of New York’s skyline. Working alongside Callahan is Rick Tepper.

Rick Tepper: I just happened to glance up and I saw a mushroom cloud coming off the first tower. We knew it was an explosion type of fire. I said, "Greg, look at that."

Callahan: He was off my left shoulder, and he points out the window and said, “Look at the World Trade Center”.

Tepper: And he’s going “Oh, my god, look at that.” And so we were just standing there staring and just in disbelief. Watching it. Watching it burn.

The initial reports: a small private plane appears to have crashed into the tower.

Bob Varcadapane was the supervisor in Newark tower that morning, in charge of eight controllers.

Bob Varcadapane: You could see the smoke billowing from the side of the building, and we didn’t know what it was. I got on the phone to the en route air traffic control facility out in New York on Long Island and I asked them if they’d lost any airplanes, and they said, “No, but Boston Center lost an airplane. They lost an American 767...”

Brokaw: Did it occur to you at that point that it could have been that plane that went into the World Trade Center?

Varcadapane: Well, that’s exactly what I said to myself then. I said to the controller that I have a burning building. And you have a missing airplane. This is very coincidental.

As Bob Varcadapane trades calls with the New York and Boston centers, a horrific realization dawns on controllers. American Flight 11, still missing from radar, finally has been found.

Word of the fate of Flight 11 quickly travels throughout the air traffic control world. Back at the New York center, all eyes are now trained on United 175, as it races over central New Jersey, clearly headed toward New York.

Dave Bottiglia: I know that an airplane has hit the Trade Center. But we’re still hoping the United was not going to do that.

Until now, controllers thought — or hoped — the plane was headed toward Kennedy airport to land. But with each second it is becoming more clear that whoever is in control of the cockpit of the United plane has a different plan. New York center alerts another nearby air traffic facility, the one responsible for lower altitude planes.

Don Krivolavy: I got a call from New York center saying we have an aircraft at 24,000 feet. “He’s not talking to anybody, we don’t know where he’s going.”

Don Krivolavy is on duty that morning. His colleagues: John Smith, John Riccardi, and Dean Yacepelli.

Krivolavy: And probably ten miles into my air space he started descending. I pointed him out to John ---

8:53 a.m.
It has been just over six minutes since American 11 hit the north tower. By now, NORAD—responsible for the defense of north American airspace—has scrambled two F-15 fighter jets from Otis air force base in Massachusetts. They streak towards New York—but already they are too late.

The rest of the country, watching on television, still believes the crash in New York is an accident. But these controllers, now watching in horror as the second plane bears down on lower Manhattan, are the first to know the awful truth.

Mark Dipalmo: I think we all knew something was going to happen, be it the Statue of Liberty, the Empire State Building.

John Smith: It was highlighted to me so that I could watch it as it came in from the southwest and then made a direct turn towards the south tower.

Brokaw: When it made that direct turn did you think, “Oh, my God?”

Smith: I thought it was a fighter jet coming in to cover the city. And it turned out he continued to descend down through 5000 feet and lower...

Jeffroy: And that’s when my supervisor came up and said, “You know, you could probably consider him a terrorist at this point.” And you kind of just turn around and got this kinda empty feeling.

Brokaw: It was helpless. You couldn’t do anything.

Jeffroy: Yeah. You know, you sit there for ten years controlling planes. For the first time in your life you don’t have any control of this at all.

At Newark tower, Bob Varcadapane is still on the phone with a controller at the New York center, and learns that a second plane has been hijacked and is almost on top of Manhattan.

Varcadapane: He says to me, “As a matter of fact, you see that target coming over the Verrazano Bridge.” I went over to the radar and looked at the radar. The Verrazano Bridge is depicted on the radar. And I looked over there and I saw the aircraft descending out of 4700 feet, 3600 feet, 2700 feet.

Greg Callahan: And I could hear him calling on altitudes. “I have a target in sight, he’s descending rapidly.” And he said—“Look out to the southeast,” and the gentleman working ground control said, “Hey, who’s that by the Verrazano Bridge?” And here comes a very large target descending rapidly, very fast.

Tepper: He was in a hard right bank, diving very steeply and very fast. And as was in he was coming up the Hudson River, he made another hard left turn and just heading for downtown Manhattan.

Varcadapane: It was fast.

Callahan: Very fast. He was moving fast.

Brokaw: Anybody in the room say anything at that point, or are you just transfixed by what you were seeing?

Callahan: Well, that pretty much confirmed all our worst fears if there’s anything in the back of your mind saying, “Maybe this just was something minor,” basically everyone—there was a moment of silence, and then things really started to move.

Tepper: You could see that he was trying to line himself up on the tower. And just before he hit the tower he almost leveled it out and just hit the building.

And I’m still talking to the center at that time. And I just said “Oh, my God he just hit the World Trade Center.” And you could see him go in the side of the building and then you just saw the flames and explosion erupting out the other side of the building.

Brokaw: What was going on in this room at that time?

Varcadapane: There was disbelief. They couldn’t believe what we just saw.

They knew it was coming, but until they saw it happen with their own eyes, it was too hard to believe. As the second strike plays out on live television, the rest of the country is also in shock, finally understanding what these controllers already knew: America is under attack.

Controllers in the tower immediately wonder could there be a third attack on the way? Supervisor Bob Varcadipane takes immediate action.

Varcadapane: I immediately went to the phone and called Washington, D.C. to tell them that Newark was ceasing operations. We were not moving any airplanes.

Brokaw: Who did you call in Washington?

Varcadapane: I called the Air Traffic Control System Command Center.

Brokaw: Do you have a hotline right to—

Varcadapane: Yes. I have a phone directly to that center. I told them that Newark was ceasing operations. We would not accept any aircraft landing at Newark Airport. My main concern was keeping airplanes out of this air space. New York City was just attacked twice. So then we shut down. I believe that was the beginning of the shutting down of the national airspace system.

As Newark controllers shut down their airport, they have no way of knowing that one of their own planes, United Flight 93, cleared for takeoff only moments before the first tower was hit, is about to face its own crisis.

As yet another air traffic control center in Cleveland, Stacey Taylor is keeping a close eye on her flights. The FAA is warning controllers to watch transcontinental flights headed west, for anything suspicious. And then, something very suspicious does happen.

Stacey Taylor: I hear one of the controllers behind me go “Oh my god, oh my god,” and he starts yelling for the supervisor. He goes, "What is this plane doing, what is this plane doing?"

I wasn’t that busy at the time, and I pulled it up on my screen. And he was climbing and descending and climbing and descending but very, gradually. He’d go up 300 feet, and he’d go down 300 feet. And it turned out to be United 93.

By this time, United Airlines has warned crews still in the air about the potential for a hijacking. Electronic messages—similar to an e-mail, have been transmitted to pilots. “Beware, cockpit intrusion” the message read.

The pilots on Flight 93 typed back, “Confirmed.” Message received.

Back in New York, controllers brace themselves for another possible assault on their airspace.

John Smith: I was wondering what else was gonna get hit? How many more times this would happen ? Where would it happen?

John Riccardi: But at that point it was, “What was next”?

9:30 a.m.At Washington’s Dulles airport controllers also on high alert. But what they don’t know is that one of their own flights is now missing: American 77.

Flight 77 has been out of contact with controllers in Indianapolis for more than 20 minutes. Fighter jets are dispatched to track the flight, but the plane already has turned east, flying back over West Virginia, toward Washington, D.C.

Todd Lewis: One of my colleagues saw a primary target moving quite fast from northwest to the southeast. Nobody knew that was American 77.

Brokaw: What did you think, it was a military flight of some kind—

Lewis: I thought it was a military flight. I thought that Langley had scrambled some fighters and maybe one of ‘em got up there.

Brokaw: It was really moving fast—

Lewis: It was moving very fast, like a military aircraft might move at a low altitude.

Brokaw: How long were you able to track what turned out to be American—

Lewis: It was heading right towards a prohibited area in downtown Washington. And that covers the Capitol and the White House. We then called the White House on the hotline, and let them know.

Controllers activate a hotline to the Secret Service—and within seconds, agents are frantically evacuating the White House. The president is in Florida, but the secret service whisks vice president Dick Cheney into an underground bunker.

Lewis: Then it turned south and away from the prohibited area, which seemed like a momentary sigh of relief. And it disappeared. But it was going away from Washington, which seemed to be the right thing.

9:38 a.m.The plane does strike, crashing into the Pentagon.

Lewis: Then there was no question that—yeah, it was a commercial flight. And you’re wondering—“We’re being attacked. What’s next?”

Washington D.C. is where United Flight 93 soon will be headed. As American Flight 77 was breaching Washington’s airspace to eventually hit the Pentagon, back in the skies over Youngstown, Ohio, Flight 93 still is on course, now airborne for more than 50 minutes.

But now, as Stacey Taylor and other controllers watch, plane begins to suddenly change altitude. And the controller working Flight 93 hears a series of horrifying transmissions from the cockpit—

Taylor: I was afraid of that flight. I see this plane climbed up from his assigned altitude of 35,000 feet to 41,000 feet. Turned around and aimed right back at where we were. And descended rapidly. And when a plane descends too fast, the computer can’t keep up with it. And you get Xs in the altitude box. So we knew he was aimed at us and descending very very rapidly. At that point I knew it was a confirmed hijacking. I didn’t know where they were going, what they were doing.

We have all shuddered at the thought of what must have been going on in the cockpits of those hijacked airliners. It turns out the Cleveland controller working United Flight 93 at the time, along with a supervisors, actually heard the sounds of the struggle in the cockpit.

Taylor: I said, "Did you guys talk to him?” He goes, “Yeah, we talked to him.” I said, “What did the pilot—?" He said, “It wasn’t the pilots,” he said, “It was the hijackers.”

I said, “The hijackers?” Are you telling me the hijackers were talking to you on the frequency?”

He said, “The pilot opened up the mike before...” We heard it all.” I said, “What—?"

Like the other three planes before it, Flight 93 makes a radical turn east, shutting off the planes transponder signal. Controllers can now only see a moving “target” on radar. They have no other flight information.

Back at Newark tower, where Flight 93 took off only an hour before, Bob Varcadipane is trading phone calls with the FAA’s central command center in Herndon, Virginia. The command center is telling him there are at least ten planes they’re still suspicious of for one reason or another — all possible hijackings.

Bob Varcadapane: When I talked to the command center again, he told me that another aircraft was being hijacked. And he said, “As a matter of fact, it’s one of your airplanes.”

Callahan: We were tracking United 93. And I was in conversation with the FBI agent and he was relaying to me that we suspect that this aircraft has now been taken over by hostile forces, described the sharp turn it made over eastern Ohio and now was heading back along southwestern Pennsylvania. And I could tell just by giving it a visual track that it was obviously heading for the Washington, D.C. area.

As Flight 93 speeds towards Washington D.C, the Federal Aviation Administration does something unprecedented in aviation history. Officials at the FAA command center order that the national airspace be completely shut down—the grounding of every single civilian plane in the sky.

Controllers in the Boston and New York areas have already landed more than 1,000 planes from the Boston and New York air corridors. There are still 3,949 planes in the air. Controllers must still land every single one; as quickly as they can; at the nearest possible airport, no matter how far from their intended destination.

The controllers begin re-routing the planes at the rate of one every second.

Brokaw: And people were landing out here in Lacrosse, Wisconsin, and Peoria, Illinois.

Varcadapane: Oh, they were landing all over the country. This whole system, basically just shut down.

Brokaw: It looks like a daisy field and suddenly it goes dark.

At the Cleveland Center, Stacey Taylor is busy diverting planes to land, but can’t stop thinking about Flight 93.

Brokaw: You’re keeping your eye on Flight 93 at this point?

Taylor: Yeah. And then the transponder came back on. We got two hits off the transponder. That’s something we’ve always wanted to know. Why did the transponder come back on?

And we’re thinking, “Oh, you know? Maybe something’s happened. Maybe this isn’t what we think it is.”

Taylor: I had another airplane that I was working. And I told him, I said, “Sir,” I said, “I think we have an aircraft down.” I said, “This is entirely up to you, but if you’d be willing to fly over the last place that we spotted this airplane—and see if you can see anything. Any smoke, anything.” And he’s like, “Yeah, we’ll do that.” So he flew over and at first he didn’t see anything and then he said, “We see a great big plume or a cloud of smoke.”

Brokaw: You knew it was down.

Taylor: We knew.

A number of heroic passengers had launched their own counterattack on the cockpit—preventing the plane from reaching its presumed target: the nation’s capital.

10:30 a.m.
In just 45 minutes, controllers have safely landed almost 2,500 planes. But there are still more than 1500 in the air and each one is a potential weapon.

The airspace above the United States is in a lock down. Controllers are furiously diverting planes to land at the nearest possible airport.

Dan D'Agastino: It was a war zone. Our skies were turned into a war zone. Everywhere you turn it was military jets and helicopters everywhere. And that’s when the reality sank in. We’re at war.

Tom Brokaw, NBC News: It was nuts.

Greg Callahan: Yeah.

11:30 a.m.
More than 3000 planes have landed safely. But, there are more than 900 still to go.

Brokaw: How did you keep the concentration on the other planes knowing what had happened here?

Don Jeffroy: It’s hard but you do it because that’s what you’re trained to do.

12:15 p.m.
Finally, four hours to the minute from when controllers lost contact with that first airliner, they have accomplished their mission. For the first time in the history of air traffic control, dating back to 1938, there is not a single civilian plane over the sky in the U.S.

Until now, there has been no time to deal with emotion. But with the airspace clear, the enormity of what has happened, the staggering loss of life hits home.

Pete Zalewski: I broke down. I mean, I just broke down.

At Boston center, Pete Zalewski, the first controller to handle a hijacked plane, maintaining composure throughout it all—he finally falls apart.

Zalewski: I started crying. I couldn’t talk. I started shaking. And I just said, “What’s wrong with the world? What’s happening?”

There is more bad news for the Boston center. One of the controller’s wives actually had been on the American Flight 11, the first plane to hit the world trade tower.

Tom Roberts: Doug McKay’s wife was on American 11. And—

Brokaw: —Was he on duty?

Roberts: Doug was actually on his way to work. Doug had dropped his wife off at the airport.

Ron: We stopped Doug at the door, and we basically took him aside and brought him into another room. And we went through—taking care of Doug. And it was pretty tragic.

Brokaw: That is part of the brotherhood and sisterhood, isn’t it? You have to take care of each other as well as take care of all those airplanes out there.

Don Jeffroy: It sure is.

The skies over America would ultimately remain closed down for three days to civilian aircraft.

Brokaw: When flights resumed and controllers came back on duty in this room after September 11th what was the tone?

Dan D'Agastino: Very somber.

For many controllers, the coming days and weeks were harder still—each shift a waiting game, with controllers wondering, “Will there be a next time?” And “If there is, will we be able to stop it?”

Dave Bottiglia: Every little thing that happened I was jumping up.

Brokaw: And any tiny little glitch would cause…

Bottiglia: Oh. The stress was enormous.

For Pete Zalewski it was difficult to come back at all.

Zalewski: For about a month I didn’t sleep. I was out of work for about six weeks, but I knew there was a point where I would go back. I needed my life back.

The shadow of that day will always hang over them.

John: Every time an aircraft doesn’t do exactly what you tell them, it brings up the thought of what could happen now and what’s gonna happen, what is he doing, why is he doing this, why is he not answering. And it brings it right back, every time.

Roberts: It’s not only planes as weapons but we’re also watching out for sensitive areas such as nuclear power plants. You know—large -

Martins: —stadiums, reservoirs—

Roberts: —bridges and stuff like that. And that’s added a new dimension to our job. We feel that we’re every bit a part of this nation’s defense when it comes to the skies, as anybody else. Because you know we’re gonna be the first line there.

Every September 11th is another painful reminder for these controllers. Many have shied away from reading about it, or watching coverage on television.

Bottiglia: I already know too much. Because I watched the American disappear, the United disappeared. And those were the first two. And I guess I’m the first one to know it.

Brokaw: It’s an honor you’d rather give up, though, right?

Bottiglia: Absolutely. I just think about all those people... and all the brave people that died there.

He remains in awe of the timing of it all.

Bottiglia: How did they do such a coordinated thing, that the American literally disappeared, and the United literally got hijacked at almost the same time. And I’ve always wondered if they were actually talking to each other saying, “I’m going in now, good luck.”

It’s the “what if’s” that plague the Newark controllers.

What if those fighter jets scrambled to intercept the second plane had arrived just a bit earlier?

Bob Varcapade: I rememember the two F-15’s. They were moments after the impact. And I was just said to myself, “If they only could’ve gotten there a couple minutes earlier. They just missed it.”

Callahan: But what would they have done?

Brokaw: What do you think they would’ve done, though?

Callahan: 20/20 hindsight—

Varcapane: I don’t know what they have done.

Brokaw: They probably would have had to shoot it down.

Callahan: But back then, that only came from the President.

Varcapane: Right.

What if Flight 93, delayed so long on the runway at Newark that morning, had been delayed just a few minutes more.

Varcapane: If it happened a few minutes later, it may not have made it off the ground. It may not have made it at all, unfortunately.

Each of them struggles with personal memories: moments, images, seared into their consciousness. They will never forget them.

Pete Ender: I still can hear their voices. That will never go away from me. Just horrific. The feeling of it. The voices, you knew they had control. You knew they had control, and we didn’t. And that was very scary. Because as controllers you’re taught to have control and there was none that day.

They were the four darkest hours in aviation history. But these controllers and their colleagues across the U.S., met an unprecedented challenge that morning five years ago: their coolness kept other tragedies from occurring, ensuring the safety of more than 350,000 people in the air, countless more on the ground.

Brokaw: I know you have professional pride but when you look back aren’t you a little astonished that it went as well as it did?

Mark Dipalmo: The people that were working that day, did a phenomenal job. I mean the controllers in this country are the best in the world and I’m proud to be one of them.

Dateline wires the home of a volunteer, Jenny, from top to bottom with hidden cameras. Then she called repairmen to her house for a simple problem we created as a test with Jenny's pool. NBC's Chris Hansen reports.